Half-tone screen



Feb. 6, 1934. A A, PEARSQN 1,945,865

HALF-TONE SCREEN Filed OCT.. l0. 1932 TEE-Z Patented Feb. 6, 1934 PATENT omas UNITED STATES 11 Claims.

This invention relates to half-tone screens and the method of manufacturing and using the same, and has particular reference to the parts of the screen and their individual characteristics which combine to create an improved, more eiilcient, and exceeding unique screen that may be employed in making half-tones, such employment producing plates of finer detail and quality because of the high interpreting power of the screen o contemplated.

One of the important aims of the instant invention is the contemplation of a half-tone screen that comprises a laminated base, whereupon is sprayed a mass of opaque blotches; said blotches being substantially uniform in thickness throughout and having their edges overhanging, whereby to present a distinct outline without the possibility of a variation in the opaqueness of any of the many blotches.

Another object of this invention-is to provide a half-tone screen having a transparent, laminated base and a mass of irregular blotches carried by one of the laminations, the important relation between supporting lamination and blotches being the cohesive force inherent in the material forming the blotches and the adhesive power which is established between blotches and supporting lamination, the former being greater than the latter, whereby to prevent "thinning", running or fading on the part of any of said blotches. f'

A yet further object of the invention is the contemplation of a method of employing the aforementioned half-tone screen in producing negatives for use in producing printing plates, which method allows controlling of high light and deep shadow intensities and the tone range therebetween.

An understanding of this art readily teaches that plates of the general character contemplated by this invention have opaque blotches thereon which are more or less transparent on account of the failure of the blotch to remain concentrated to a suiiicient degree when it is applied to the base and during the time it is drying.

Such shortcomings of half-tone screens as are mentioned above are always found when the relation between materials is not considered. As a matter of fact, the practice is not to establish any useful relation between the component parts of the half-ton'e screen other than that which naturally occurs and, as a result thereof, objectionable screens are produced.

It is, therefore, the object of this invention to produce half-tone screens which overcome such shortcomings to the extent that marked improvements as to clearness, detail and tone shading are noticeable in the printing plate produced through the use of a half-tone screen embodying the concepts of this invention, such detail and shading being controlled by the duration of exposure to allow more or less action upon the sensitizng of ,the plate behind the opaque blotches of the screen.

A half-tone screen made in accordance with the present invention is diagrammatically illustrated in the accompanying drawing, wherein:

Figure 1 is a face view of a half-tone screen greatly emerged for clearness.

Fig. 2 is a cross section through the screen, and,

Fig. 3 is an enlarged, fragmentary, cross sectional view showing in detail the relation of parts and general character thereof.

Fig. 4 is a diagrammatical showing of the manner of making a negative by the method contemplated through the use of the unique screen.

In producing a screen such as this invention contemplates, materials used play an important part. A transparent plate 6 of glass or similar substance is used as a foundation for one oi' the superimposed layers of material which constitute the base of the screen.

Upon this plate 6 there is placed a coating or layer of material 8 which presents an outer surface 10 that is irregular to the extent that a tooth is formed which assists in setting up the necessary adhesive force when the hereinafter described blotches are applied. Coating 8 is non-absorptive, does not remain tacky, and must not be composed of albuminous or oily substance such as is now so commonly utilized in this art. This coating 8 may be made in many ways so long as the relation between later described blotches and said coating 8 meets the requirements of this invention. A coating including sandarac or a similar resinous substance having shellac or like ingredients has been found suitable. This coating 8 must be entirely drybefore the next step of the method of forming a half-tone screen is taken. Blotches 12 are formed upon coating 8 by spraying an opaque liquid thereon. Such spraying should be done through the use of an adjustable spray gun and when the mass of blotches 12 are in place, they should be exceptionally irregular and ramied in form and without any thin areas.

It is, therefore, absolutely necessary that opaque substance be used which has a cohesive property that is greater than the adhesive force set up between blotches 12 and coating 8 when the materials are brought together. Ordinarily, the well known 'commercial water-proof drawing ink may be used as the liquid opaque substance which forms blotches 12. It is necessary to guard against the absence of pigment in the liquid, however, and since blotches 12 are exceedingly thin, caution must be exercised in` this regard.

The relation between the cohesive property of the liquid blotches and the adhesive force set up between blotches 12 and coating 8 should be as previously mentioned. This combination will preclude spreading or running of blotches 12 after l they have struck surface 10 of coating 8. Blotches l very edge in order to allow desired control.

12 should remain over that area covered in the instant of application, and since there is a tendency of blotches 12 to bulge or pull outwardly from the main body, the edges of each blotch 12 will slightly overhang as at 14. Such overhanging merely assists in creating a clean cut outline to the blotch 12 and likewise insures that the thickness of blotches 12 is substantially the same throughout. f

Ramied, transparent areas are created between blotches 12 and it is desirable to have said mass of blotches covering over fty percent of the total area of the half-tone screen. Manifestly, coarse or line screens may be made simply by adjusting the spray gun and altering the size of the blotches. In producing coarse screens the blotches are larger and less air is admitted at the spray nozzle of the gun. In making fine screens, more air is admitted and the blotches are smaller in size.

After the blotches are thoroughly dry, a very thin coating of transparent material may be placed thereover to protect the same against scratches or other destructive action during use.

After the screen has been made as above described, it should be used with a dry plate or film by directly contacting the same against the sensitized coating 16 thereof. The base 18 of this plate is of glass or ordinary celluloid or similar substance and is, obviously, transparent. A negative is produced by photographing the image 20, that is to be reproduced, through a camera having a lens 22. In this method thel side of the screen bearing blotches 12 is placed in direct contact with sensitizing 16 and the exposure made upon this sensitizing through the screen. It is imperative that the length of exposure be correct to procure the desired detail.

It is always desired to expose long enough to cause creeping" of the light inwardly from the edges of the blotch 12 in the high-light areas, whereby to break the distinct line established thereby. The edges must be distinct and the individual blotch must be entirely opaque to the If the blotches lost their opaqueness as the edges were approached, control in exposure would be impossible. Prolonging the time of exposure causes more of the sensitizing behind the blotches to be acted upon by light passing through the screen and with the two factors, i. e., clean out, opaque-to-edge blotches and directly contacting blotches and sensitized coating always present,

it is possible to produce negatives of exceptionally high interpreting value. 'I

Having thus described the invention, what is claimed as new and desired to be secured by Letters Patent is: 1. A half tone screen of the character described comprising a base; anda mass of irregularly positioned blotches of opaque liquid on one side thereof, the inherent cohesive property of saidv liquid blotches being of greater intensity than the adhesive force between the base and blotches whereby the depth of the latter is substantially uniform throughout.

2. A half tone screen of the character described comprising a base; and a mass of irregularly positioned blotches of opaque liquid on one side thereof, said base consisting of superimposed layers of transparent material, the layer directly adjacent said blotches having an adhesive attraction for said blotches of less intensity than the inherent cohesive property of said blotches, whereby the thickness of said blotches at their edges is substantially equal to the thickness throughout the body thereof.

3. A half tone screen of the character described comprising a plate of transparent material; a coating of non-absorptive, transparent material superimposed upon one side of said plate; and a mass of opaque blotches upon said coating, said blotches being securedin place by the inherent adhesive forces of said coating and blotches, the latter being'substantially uniform in thickness throughout.

4. A half-tone screen of the character described comprising a plate of transparent material; a coating of non-absorptive, transparent material .superimposed upon one side of said plate; and a mass of opaque blotches upon said coating, said blotches being secured in place by the inherent adhesive forces of said coating and blotches, the edges of said blotches overhanging and being substantially the same thickness as the remaining portion of the blotches.

5. A half -tone screen of the character described comprising a plate of transparent material; a coating of non-absorptive, transparent, toothforming material overlying one side of said plate; and a mass of opaque, ramied liquid blotches on said coating, said blotches being confined to the area covered when formed on said coating and being substantially uniform in thickness throughout.

6. The method of making half-tone screens of the character described consisting in applying a coating of non-absorptive, transparent material to a transparent plate, and spraying opaque liquid over said coating in the form of a mass of irregular blotches of uniform thickness.

7. The method of making half-tone screens of the character described consisting in applying a coating of non-absorptive, transparent material to a transparent plate, and spraying opaque liquid over said coating in the form of a mass of irregular blotches of uniform thickness, said opaque liquid having inherent cohesive property of greater intensity when said blotches are positioned than the adhesive force between said coating and blotches.

8. The method of producing a negative for use in making a printing plate, consisting in photographing the image to be reproduced upon a sensitized plate through a screen having a mass of irregularly positioned blotches of opaque material on one side thereof, the said sensitized plate and screen being in direct contact.

9. The method of producing a negative for use in making a printing plate, consisting in photographing the image to be reproduced upon a plate, sensitized on one side, through a screen having a mass of irregularly positioned blotches of opaque material on one side thereof, the`said sensitized side of the said plate and opaque material of the said screen being in direct contact.

10. The method of producing a negative for use in making a printing plate, consisting in photographing the image to be reproduced upon a plate, sensitized on one side, through a screen having a mass ofirregularly positioned blotches of opaque material on one side thereof, the said sensitizedv side of the said plate and opaque material of the said screen being in Contact, the exposure of said plate being of su'cient duration to cause action upon the sensitizing thereof inwardly from the edges of said superimposed blotches.

11. The method of producing a negative for use in making a printing plate, consisting in photo- 

